The increasing incidence of ADHD diagnosis and its uneven prevalence across demographic groups has sparked debates about misdiagnosis. We use data on individuals' genetic predisposition to ADHD from the Add Health survey of U.S. schools to uncover relative standards in ADHD diagnosis. We estimate that students' ordinal rank in the genetic predisposition to ADHD among their same-gender school peers has a positive, statistically significant, and substantial causal effect on ADHD diagnosis, holding students' own genetic predisposition to ADHD constant. This effect is mainly driven by boys, contributing to explain the observed higher rate of diagnosis for boys relative to girls.